Method of recycling iron-bearing waste material back into a basic oxygen furnace

ABSTRACT

The invention is directed to a process for dehydrating and recycling back into a BOF converter wet BOF scrubber sludge to produce a steelmaking revert having an improved flow rate when handled in a recycle stream. Wet sludge is combined with hot BOF slag to provide a slag/sludge mixture. The wet sludge causes the mixture to have a moisture content greater than 10% water by weight, and the hot slag, having a temperature below the molten liquid state, vaporizes the water in the mixture and reduces the moisture content to about 4% water by weight or less. The dehydrated mixture has improved flow rate properties when it is recycled as a steelmaking revert.

This application is a continuation-in-part of application Ser. No.08/835,168, filed Apr. 8, 1997, now U.S. Pat. No. 5,785,737.

BACKGROUND OF THE INVENTION

The invention is related to a method for recycling iron-bearing dustsand sludges back into a steelmaking process, and more particularly, itrelates to a method for recycling iron-bearing waste materials back intoa basic oxygen furnace (BOF) simultaneous with the oxygen blow used inthe process of converting molten iron into steel.

It is well known in the art of steelmaking that iron-bearing dust andsludges, generated by steelmaking furnaces, are valuable revertmaterials suitable for recycling back into steelmaking operations. Suchwaste materials contain iron oxides in an amount up to about 50% byweight, and it is very desirable to recover the iron for use as asteelmaking charge material. However, in the case of wet sludges, andespecially in the case of wet BOF scrubber sludge, high moisture contentmakes the wet sludge very difficult to handle in a recycling stream.

Filter cake produced from wet scrubber sludge typically has a moisturecontent of about 30% by weight. The high viscosity of such wet sludgescauses them to have poor handling characteristics. They stick toconveyors and machinery when attempts are made to convey them as revertsin a recycling stream. They move poorly and often form stickyagglomerations that clog and shutdown equipment and machinery. Forexample, under test conditions, it has been found that wet sludge havinga moisture content of >10% has a flow rate of less than 10 pounds ofsludge per minute. Such low flow rates make wet material very unsuitablefor recycling as a steelmaking revert.

In instances where waste steelmaking dust is recycled back into theoperation, the dry powdery condition of the material causesenvironmental dusting problems. To control dusting either water is addedor the dry material is mixed with wet sludges to eliminate the dusting.However, when various different wet or dry waste materials are combinedto produce a steelmaking revert, high levels of undesirable elements andcompounds can be introduced into the steelmaking process. For example,if hot dip coating sludge is introduced into the recycling stream, thezinc in the recycling stream can rise to a level where the wastematerial is unsuitable for use in a steelmaking furnace. Therefore, suchcombining of steel plant wastes must be carefully monitored forchemistry to avoid introducing deleterious elements into the steelmakingprocess.

Various apparatus and methods have been developed in the past to reducethe moisture content and/or recover iron from wet sludges. For example,U.S. Reissue Pat. No. 30,060 teaches a process that instantaneouslyvaporizes the water in sludge by spraying the sludge into a hot (1200°F.) gas stream. U.S. Pat. Nos. 4,091,545 and 4,133,756 also teach usinga hot gas to reduce the moisture content of wet sludge.

U.S. Pat. Nos. 5,114,474, 4,725,307, 4,711,662 and 2,710,769, teachmixing wet sludges and dust with molten slag to produce reverts. Themixture is crushed for recycling after the slag cools and solidifies.

An article in "33 METALPRODUCING," March 1997, discloses a process thatforms BOF waste sludge into briquettes. The apparatus used in theprocess includes a rotary kiln or dryer to remove water from the sludge,a roll-press, screw conveyors and pug mills. Such recycling plantsrequire large capital investments. The use of a rotary kiln consumesexpensive energy to generate heat for drying the sludge. The articlealso discloses using heated molasses as a binder to form the briquettes.The heated molasses also adds cost to the recycling process.

In the February 1997 issue of "NEW STEEL", an article by John Schrieferentitled Reaping the value from dust and slag, discloses that 11 steelmills located throughout Indiana and Ohio generated 959,000 tons of wetBOF sludge during the year 1992. In an effort to reduce landfill costsassociated with disposing of such sludge, and in an effort to recoverthe valuable metallic materials contained in the sludge, such sludge isprocessed into briquettes for recycling back into a BOF as a source ofiron. The article further mentions that such iron-bearing briquettesreplace some of the steel scrap used in the BOF steelmaking process.Therefor, from a steelmaking viewpoint, it would appear reasonable thatthe article teaches charging the iron-bearing briquettes into the BOFvessel prior to the molten iron charge.

U.S. Pat. No. 3,870,507 to Allen is also directed to forming iron oxidebriquettes. However, the Allen briquettes are recycled into a blastfurnace with new iron making materials. Steelmakers are reluctant tocharge such briquettes, dusts and sludges, back into steelmakingfurnaces because steelmaking wastes usually contain high levels of heavymetals, for example zinc, and they adversely affect the quality of thefinished steel product.

Finally, U.S. Pat. No. 5,496,392 to Simms, et. al. is directed to amethod of recycling industrial waste. The recyclable iron-bearingmaterial is either pelletized or formed into briquettes. The patentteaches that such briquettes are charged cold into a steelmaking furnaceand heated up to temperature. The patent is absent of any teaching thatwould suggest charging such iron-bearing reverts into the vesselsimultaneous with the oxygen blow.

Therefore, as shown in the patents, it is well known within thesteelmaking art that steelmaking sludges and dusts can be processed andrecycled as valuable reverts. It is also well recognized that wetsludges flow poorly and create logistical problems within a recyclingstream because of their poor flow rate properties. The patents alsoteach that dry steelmaking waste materials present dusting problemsduring recycling. Finally, the above patents teach solving thesewell-known problems by dehydrating wet sludges with hot gases to producea suitable sinter or charge material. The current state-of-the-artrequires complex recycling facilities and hot gas blowers that consumelarge amounts of expensive energy to dry wet sludges. The hot gasvaporizes the water in the wet sludge and reduces the moisture contentof the sludge to a level where the sludge can be used as a steelmakingrevert.

SUMMARY OF THE INVENTION

Therefore, the primary object of the disclosed invention is to provide aprocess for dehydrating and recycling wet steelmaking sludges asiron-bearing reverts back into a BOF converter during the process ofconverting molten iron into steel. The process includes the steps ofcombining wet sludge and hot slag into a hot slag/sludge mixture;resting the hot slag/sludge mixture for a period of time to allow thehot slag to cause water vaporization and reduce the moisture content ofthe slag/sludge mixture to less than 10% by weight. The dehydratedslag/sludge mixture is recycled as a steelmaking revert back into thesteelmaking vessel subsequent to the molten iron charge, andsimultaneous with the oxygen blow that reduces the carbon content of themolten metal bath contained in the vessel.

These and other objects and advantages of the invention will be readilyapparent in view of the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating the steps of the process fortreating wet steelmaking sludge to produce a steelmaking revert.

FIG. 2 is a graph showing flow rate measurements in relation to sludgemoisture content.

FIG. 3 is a graph showing steel analyses for finished BOF heats producedaccording to the steps of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 of the drawings, modern steelmaking pollutioncontrol devices such as bag houses, precipitators, cyclones andscrubbers generate large quantities of iron-bearing dusts and sludges.Such waste materials are valuable reverts for charging back into thesteelmaking furnaces. However, many of these waste materials are veryhigh in water content due to the wet environmental processes, such aswet scrubbers, that are used to control steelmaking emissions.

In the preferred embodiment, FIG. 1 shows a basic oxygen furnace (BOF)10 and hood 11 positioned above the mouth of the BOF to collect fume andgas that is emitted during the steel refining process. The fume and hotgasses are collected in a wet scrubber 12 and the wet scrubber sludge issent to a thickener 13 where water is removed. A further downstream stepin the recycling process typically includes either batch or continuousfiltration of the wet sludge. This filtering step is carried out inpress 14 where a wet filter cake 15 is produced. The filter cake, orsludge, has a moisture content of about 30% water by weight.

As heretofore mentioned, wet BOF sludge contains iron oxides in amountsof up to about 50% by weight, and it is very desirable to recover theiron for reuse as a charge material in the steelmaking operation.However, the high viscosity of the wet sludge makes it very difficult tohandle the material as a steelmaking revert. It has been discovered thatif the moisture content of the wet sludge can be reduced to less thanabout 10% water by weight, the flow rate properties of the sludge isimproved to where the sludge can be conveniently handled as asteelmaking revert. Is has also been discovered that a preferredmoisture content of between about 3-4% water produces a superior sludgeflow rate as a revert.

For example, in the graph shown in FIG. 2, flow rate is plotted againstthe moisture content of four different mixture ratios ranging from aslag/sludge ratio of 0.05:1 up to a ratio of 10:1. The flow rate testswere conducted in a 2 cubic foot bin having a 65°-sloped floor todischarge the slag/sludge mixture through a 21/2 square inch opening inthe bin. The plotted data in FIG. 2 clearly shows that at a preferred1:1 ratio, the slag/sludge flow rate decreases rapidly when the moisturecontent of the mixture exceeds 7% water by weight. Above about an 8%water content the flow rate of the material is considered onlymarginally acceptable, and above 10%, the material flow rate isunacceptable. Above 10%, the flow rates become very poor, and at amoisture content above 11% or higher, there is no material flow.

It can be seen that in order to use wet BOF sludge as a revert in asteelmaking process, it is necessary to first reduce the moisturecontent of the wet sludge to a level where the water in the sludge isless than 10% by weight. And as clearly shown in FIG. 2, the water levelfor all four tested mix ratios should be reduced to a preferred range ofbetween about 3-4% to achieve optimum flow rates as shown in the plotteddata. It has also been discovered, during actual use in a pilot test,that when the moisture content of the wet sludge material falls to alevel below 3% dusting can become a problem. If this happens, water mustbe added to the slag/sludge mixture to bring the moisture content backup into the preferred 3-4% moisture range to eliminate dusting.

Dehydrating wet sludge is extremely energy intensive. The prior patentsdisclose sludge drying operations that consume large amounts of energyto generate heat for vaporizing the water in the sludge. It has beendiscovered that hot slag, at a temperature below the molten liquidstate, provides a free heat source that can be combined with the wet BOFsludge to vaporize the water and lower the moisture content of thesludge.

As heretofore disclosed, the prior patents teach mixing molten slag withsteelmaking dusts and sludges to recover iron from steelmaking waste.Such practice is extremely dangerous. Mixing molten slag with water cancause terrifying explosions. In the past, such explosions at steelmakingoperations have resulted in injury and death to employees. The priorpatents even warn of this problem. For example, Pinkerton discloses, inU.S. Pat. No. 2,710,796, that "Excessive water, however, must beavoided; the generation of steam is too violent . . ." Explosiveconditions are completely avoided when hot, not molten, slag is combinedwith wet sludge to drive off water from the sludge.

Referring again to FIG. 1, hot slag from supply 16 is combined with wetsludge from supply 15 to form a hot slag, wet sludge mixture at 17. Thepreferred and most convenient method for combining the hot slag and wetsludge is to blend alternating batches taken from the supplies 15 and16. This produces the preferred 1:1 slag/sludge mixture ratio. However,it has been discovered that careful blending of the hot slag and wetfilter cake or sludge is required to avoid rapid steam generation. Theprocedure developed to avoid rapid steam generation involves combiningthe materials into a stratum comprising alternating 1-2 feet thicklayers of slag and wet filter cake or sludge. This procedure allows forsafe evolution of steam and uniform drying of the filter cake or sludge.Reclaiming the layered pile 17 after curing for about 16 hours resultsin a uniform blend of the two materials suitable for any down streamprocessing, i.e., crushing screening, and/or magnetic separation. Thisprocedure is readily done with front-end loader bucket used at most slagprocessing sites in the steel industry.

The slag/sludge mix rate can be changed to produce slag/sludge ratios upto about 10:1 or down to about 0.5:1. However, when the slag/sludgeratio is changed to increase the slag content in the mixture themetallurgical impact on finished product quality must be considered. Itmust be remembered that slag additions reintroduce removed impuritiesback into the steelmaking vessel. For example, in most instances,phosphorus is considered detrimental with respect to the quality ofsteel products. Metallurgists attempt to entrap phosphorus, and otherimpurities, within the slag cover that floats on the surface of themolten steel bath contained in a steelmaking vessel. These impuritiesare removed from the molten steel as the slag is systematically tapped.

                  TABLE A                                                         ______________________________________                                        SLAG/SLUDGE 1:1 RATIO                                                         CHEMICAL ANALYSIS                                                             Symbol, % db                                                                             Slag/Sludge BOF Slag BOF Sludge                                    ______________________________________                                        Fe         41.0        21.4     60.9                                          Mn                                          0.86                              P                                           0.06                              Zn                                         1.4                                SiO.sub.2                       12.5                                                                                       1.4                              CaO                                          4.6                              MgO                                          1.6                              Al.sub.2 O.sub.3                                                                                                           0.1                              TiO.sub.2                       --3                                                                                       0.06                              ______________________________________                                    

Table A shows the chemistry for a 1:1 slag/sludge mixture combined fromBOF slag and BOF scrubber sludge. The table shows that the slag containsabout 0.7% phosphorus by weight and the sludge contains about 0.06%phosphorus. The resulting combined mixture has about 0.3% phosphorus ata 1:1 slag/sludge mixture ratio. This is an acceptable phosphorus levelfor BOF charge material. If the 1:1 mixture ratio is changed to increaseslag content, the phosphorus level will increase. For example, if theslag taken from supply 16 is combined with sludge from supply 15 at a2:1 slag/sludge ratio the slag/sludge mixture will contain about 0.49%P, at a 5:1 ratio the mixture will contain about 0.59% P, and at a 10:1ratio it will contain about 0.64% phosphorus.

After the slag/sludge mixture is dehydrated to the desired 3-4% moisturerange its flow rate properties are improved, and it is sent downstreamfor additional processing. These additional processing steps can includemagnetic separation 19, screening 20 and/or sintering 21. In mixturesthat contain high zinc levels of about 0.9% and above, the mixture isnot considered suitable for use in a sinter bed operation 21, and suchslag/sludge mixtures are charged directly into the BOF with or withoutmagnetic separation and/or screening as shown by lines 22 and 22a. Inslag/sludge mixtures where the zinc concentration is lower than about0.9% by weight, the mixture can be added to the sinter bed 21 with orwithout magnetic separation and/or screening as shown by lines 23 and23a. However, it should be understood that low zinc level slag/sludgemixtures could be charged directly into a BOF without sintering.

It has been discovered that fine particles, about 20 mesh (˜0.03 in.),in the reclaimed slag/sludge mixture that has particles ranging up toabout 0.5 inch in size, can present a problem if the slag/sludge revertis charged directly into a BOF. It has also been discovered that suchfine particles can be feed directly into a sinter plant withoutpresenting any known problems in the sintering operation. When thesmaller 20 mesh slag/sludge fines are charged directly into a BOF, theyare carried out of the vessel with the off gases. This overloads the gascleaning scrubber system and negates the recycling effort.

In order to solve this problem, lime can be added to the wet filter cakeor sludge 15 in an amount of about 1% by weight. It is believed that thelime addition causes micro-pelletization of the slag/sludge fines duringcrushing and screening operations down stream from the blending processshown at 17. The many conveyor to conveyor transfer points, and thevarious water sprays located throughout a recycling operation, cause thelime to act as a binder and enhance agglomeration of the slag/sludgefines into micro-pellets. This reduces the amount of 20 mesh fineswithin the dried slag/sludge mixture and makes the revert more suitablefor charging directly into a BOF vessel.

Under actual plant conditions, the lime blended, agglomeratedslag/sludge mixture was charged into a BOF without any noticeableincrease of fines in the off gases. The lime blending technique alsoreduced dusting problems during handling and charging of the blendedmaterial. As a result, the moisture content of the slag/sludge mixturecan be further reduced to a preferred range of between about 2-4% waterby weight when lime additions are blended with the filter cake.

Modern steelmaking requirements make it necessary for BOF operators toaccurately calculate the exact weight of raw materials, and selectvarious raw materials required for producing a given heat. Thesecalculations and selections are based upon the specifications for thedesired finished steel product. Utilizing data provided by theoperators, computers calculate the required weights of molten iron andsteel scrap needed for the particular heat, and the computer determinesthe proper amount of oxygen that will be blown into the molten metalbath to reduce the carbon content of the iron to a proper level for thesteel grade. In the past, steelmakers have attempted to include in thecalculations small amounts of iron-bearing reverts in an effort torecycle steelmaking waste back into the BOF steelmaking process. Suchreverts are typically charged into the BOF vessel along with the coldsteel scrap as disclosed above by Schriefer and Allen. However,heretofore, only small amounts of iron-bearing waste or reverts could berecycled back into the BOF, for example about 10% of the waste producedby the steelmaking process, because such waste typically contains heavymetals, for example zinc, that adversely affect the finished steelproduct.

The computer also calculates amounts of iron ore by weight for charginginto the BOF during the oxygen blow. The iron ore functions as a coolantthat reduces or maintains a desired temperature in the vessel. As thehigh velocity oxygen stream is injected into the molten iron it reducesthe carbon content of the bath and converts the molten iron to steel.During the reaction, temperatures within the vessel are elevated as theinjected oxygen removes carbon from the bath. The additional iron orecharge during the O₂ blow has a cooling affect on the reaction andprevents temperatures from reaching undesirable levels. It has beendiscovered that if the slag/sludge revert produced by the steps of thepresent invention is blended with the iron ore and charged as a coolantduring the blow, the heavy metals contained in the revert areinstantaneously vaporized and have little detrimental affect on thequality of the finished steel. Because of this discovery, greateramounts of steelmaking waste can be recycled as iron-bearing revertsback into the BOF steelmaking process, for example about 80% and higherof the total waste material produced by the steelmaking process. Therevert/ore mixture is blended together at a rate or ratio based upon theiron content in the revert to the iron content in the iron ore. Forexample, if analyses shows a concentration of 45% Fe by weight in therevert, and a concentration of 65% Fe by weight in the iron ore, theamount of revert to ore is 45/65, or about one pound of revert to every0.7-pounds of iron ore. The amount of recycled revert material is alsoadjusted for its slag content as well as for the valance state of theiron contained in the revert. The degree of reduction that will takeplace for the revert is directly related to the valance of the ironpresent in the material, i.e. the Fe⁰, Fe⁺², and Fe⁺³ present in therevert affects the chemistry of the finished steel.

When iron-bearing revert material, whether in briquette form or ingranular form, are recycled back into a BOF vessel subsequent to themolten iron charge and simultaneous with the oxygen blow, theundesirable non-ferrous compounds contained in the revert material areinstantaneously vaporized by the hot reactive temperatures and the highcarbon atmosphere generated during the oxygen blow. Heavy metals, suchas zinc, cadmium, etc., are volatilized in the presence of carbon. Forexample, in the case of zinc and zinc oxides, CO and CO₂ rich atmosphereabove the hot molten metal bath has a temperature range of between2400-3000° F., the carbon in the atmosphere reacts with zinc oxides inthe revert material to remove oxygen and leave behind zinc metal thatinstantly fumes out in the high temperature through the BOF exhausthood. Similarly, cadmium oxide will volatilize before reduction and fumeout through the exhaust hood. The remaining iron revert/ore mixture isreduced to steel and combines with the product in the molten metal bath.

As shown in FIG. 3, charging iron-bearing revert material back into aBOF converter simultaneous with the oxygen blow avoids contaminating thefinished steel product with heavy metals such as zinc. In actualpractice, revert material containing zinc concentrations of up to about200,000 ppm zinc by weight was recycled back into the converter. Theplotted data shows that when such iron-bearing reverts are charged intoa BOF, according to the steps set forth in the present invention(simultaneous with the oxygen blow) the mean level of zinc contained inthe finished steel product is about 21 ppm, showing no adverse impact onthe zinc content of the steel. We have also discovered that it is bestto charge the revert/ore mixture early in the heat. Improved resultsappear to be achieved when the revert/ore mixture is charged withinabout one minute after the oxygen blow begins, or after about 23,000cubic feet of O₂ is blown into the heat. This is because more completereduction of the oxides contained in the revert is able to take place inthe atmosphere above the bath due to the abundance of the CO and CO₂generated during the initial stages of the O₂ blow. However, it has beenfound that revert/ore mixtures can be introduced into BOF converters atany time during the oxygen blow if they are introduced within a chargerange that begins after about 20,000 cubic feet of O₂ is blown and endsafter about 66,000 cubic feet of O₂ is blown into the heat, i.e. up toabout 2.5 minutes from the start of the oxygen blow. The charging timefor such revert/ore mixtures are between about 15 to 30 seconds to dumpthe entire batch into the furnace. The amount of iron-bearing revert inthe charge can vary in weight up to about 15,000 pounds per heatdepending on operating conditions. To accomplish a revert/ore charge,the BOF charging bin (not shown in the drawings) is filled with apredetermined amount of charge materials in the following order: 1) acalculated amount of iron ore based upon its iron content, 2) acalculated amount of revert material also based upon its iron content tosatisfy, for example, the 1/0.7 revert/ore ratio disclosed above, and 3)a calculated amount of flux such as lime, limestone, dolomite, fluorite,etc. In past practice, steelmakers have chosen not to recycle granularrevert material back into a steelmaking furnace to safeguard againstproducing a finished steel product outside specification.

It should be understood, that although the preferred embodimentdiscloses charging the slag/sludge revert produced by the steps of thepresent invention, any suitable iron-bearing revert can be charged intoa BOF vessel as a revert/ore mixture without departing from the scope ofthis invention. In addition, it should also be understood that theslag/sludge manufacturing process is not limited to steelmakingoperations. Any hot dross can be used as a heat source to dehydrate wetsludge produced in any metal refining or smelting operation, and thatsuch dross/sludge mixtures can be recycled back into their respectiverefining or smelting operations.

While this invention has been described as having a preferred design, itis understood that it is capable of further modifications, uses, and/oradaptations following in general the principle of the invention andincluding such departures from the present disclosure as come withinknown or customary practice in the art to which the invention pertains,and as may be applied to the essential features set forth herein, andfall within the scope of the invention limited by the appended claims.

We claim:
 1. A process for dehydrating a wet sludge to produce a revertfor recycling back into a steelmaking furnace, the dehydrating stepsproducing a revert having an improved flow rate when handled in arecycle stream, the steps of the process comprising:a) combining wetsludge with hot slag to provide a slag/sludge mixture having a moisturecontent greater than 10% water by weight, the hot slag having atemperature below the molten liquid state; b) discontinuing said step ofcombining wet sludge and hot slag and resting the slag/sludge mixturefor a time period to enable radiant energy emitted from the hot slag tovaporize water in the slag/sludge mixture to produce a dehydratedslag/sludge mixture having a reduced moisture content of about 10% waterby weight or less; and charging the dehydrated slag/sludge mixture intoa furnace during a steelmaking oxidation phase so that oxidation phasetemperatures volatilize heavy metals in the dehydrated slag/sludgemixture and remaining iron-bearing materials in the dehydratedslag/sludge mixture fall into and become entrained within the moltenmetal bath.
 2. The process recited in claim 1 wherein step c) includescharging up to 15,000 pounds of said slag/sludge mixture into the heat.3. The process recited in claim 1 wherein said revert is charged withina range not greater than about 3 minutes after the O₂ blow begins. 4.The process recited in claim 3 wherein said revert is charged about oneminute after the O₂ blow begins.
 5. The process recited in claim 1wherein said revert is charged within a charge range that begins afterabout 20,000 cubic feet of O₂ is blown and ends after about 66,000 cubicfeet of O₂ is blown.
 6. The process recited in claim 5 wherein saidrevert is charged after about 23,000 cubic feet of O₂ is blown.
 7. Theprocess recited in claim 6 wherein said revert/ore mixture is mixed at acalculated ratio based upon iron content in said revert and iron contentin said iron ore.
 8. The process recited in claim 7 wherein saidrevert/ore mixture is mixed with a flux and charged into the steelmakingfurnace simultaneous with the O₂ blow.
 9. The process recited in claim 8wherein said flux is lime.
 10. The process recited in claim 1 whereinsaid revert is mixed with iron ore to form a revert/ore mixture chargedinto the steelmaking furnace simultaneous with the O₂ blow.
 11. Aprocess for recycling iron-bearing waste material back into asteelmaking furnace heat, the steps of the process comprising:a)charging steel scrap into the steelmaking furnace; b) charging molteniron into the steelmaking furnace; c) blowing O₂ into the molten ironcontained in the steelmaking furnace; d) charging an iron-bearing wastematerial derived from slag and sludge into the steelmaking furnaceduring the O₂ blow, the waste material having a moisture content ofabout 10% by weight or less water; e) volatilizing and dischargingthrough a furnace exhaust non-ferrous materials contained in saidiron-bearing waste material; and f) reducing to steel ferrous materialscontained in the steelmaking furnace.
 12. The process recited in claim11 wherein step d) includes charging up to 15,000 pounds of saidiron-bearing waste material into the heat.
 13. The process recited inclaim 11 wherein said iron-bearing waste material is charged within arange not greater than about 3 minutes after the O₂ blow begins.
 14. Theprocess recited in claim 13 wherein said iron-bearing waste material ischarged about one minute after the O₂ blow begins.
 15. The processrecited in claim 11 wherein said iron-bearing waste material is chargedwithin a charge range that begins after about 20,000 cubic feet of O₂ isblown and ends after about 66,000 cubic feet of O₂ is blown.
 16. Theprocess recited in claim 15 wherein said iron-bearing waste material ischarged after about 23,000 cubic feet of O₂ is blown.
 17. The processrecited in claim 11 wherein said iron-bearing waste material is mixedwith iron ore to form a revert/ore mixture charged into the steelmakingfurnace simultaneous with the O₂ blow.
 18. The process recited in claim17 wherein said revert/ore mixture is mixed at a calculated ratio basedupon iron content in said iron-bearing waste material and iron contentin said iron ore.
 19. The process recited in claim 18 wherein saidrevert/ore mixture is mixed with a flux and charged into the steelmakingfurnace simultaneous with the O₂ blow.
 20. The process recited in claim19 wherein said flux is lime.
 21. A process for recycling iron-bearingwaste materials, having concentrations of not more than about 200,000ppm zinc by weight, back into a steelmaking furnace and producing a heatof finished steel product having a concentration of less than about 43ppm zinc by weight, the steps of the process comprising:a) chargingsteel scrap into the steelmaking furnace; b) charging molten iron intothe steelmaking furnace; c) blowing O₂ into the molten iron contained inthe steelmaking furnace and reducing the molten iron to a steel product;d) charging an iron-bearing waste material derived from slag and sludgecontaining zinc into the steelmaking furnace during the O₂ blow, thewaste material having a moisture content of about 10% by weight or lesswater; e) volatilizing and discharging through a furnace exhaust zinccontained in the iron-bearing waste material; f) reducing to steelferrous materials contained in the iron-bearing waste material, thereduced ferrous materials being combined with the steel product in thesteelmaking furnace; and g) tapping the combined steel product, thecombined steel product having a zinc content of less than 43-ppm zinc byweight.
 22. The process recited in claim 21 wherein step d) includescharging up to 15,000 pounds of said iron-bearing waste material intothe steelmaking furnace.
 23. The process recited in claim 21 whereinsaid iron-bearing waste material is charged within a range not greaterthan about 3 minutes after the O₂ blow begins.
 24. The process recitedin claim 23 wherein said iron-bearing waste material is charged aboutone minute after the O₂ blow begins.
 25. The process recited in claim 21wherein said iron-bearing waste material is charged within a chargerange that begins after about 20,000 cubic feet of O₂ is blown and endsafter about 66,000 cubic feet of O₂ is blown.
 26. The process recited inclaim 25 wherein said iron-bearing waste material is charged after about23,000 cubic feet of O₂ is blown.
 27. The process recited in claim 21wherein said iron-bearing waste material is mixed with iron ore to forma revert/ore mixture charged into the steelmaking furnace simultaneouswith the O₂ blow.
 28. The process recited in claim 27 wherein saidrevert/ore mixture is mixed at a calculated ratio based upon ironcontent in said iron-bearing waste material and iron content in saidiron ore.
 29. The process recited in claim 28 wherein said revert/oremixture is mixed with a flux and charged into the steelmaking furnacesimultaneous with the O₂ blow.
 30. The process recited in claim 29wherein said flux is lime.